组合脉冲压裂加载过程耦合模拟及火药配比影响敏感性分析

基于组合脉冲压裂物理过程，以三种燃速火药柱串联、中心管同步点燃方式，结合火药爆燃加载、压挡液柱运动、射孔孔眼泄流、裂缝起裂、高压气体裂缝内流动及裂缝扩展等子模型，组建多级爆燃压裂耦合模拟模型。并据此分析不同配比火药组合爆燃压裂时，井底压力变化及裂缝延伸情况。结果表明:不同燃速火药串联组合可实现一级火药快速爆燃，瞬间达到多方向射孔孔眼起裂压力，二、三级火药持续长时间燃烧维持高压以充分延伸裂缝的目的；在确定一级快速火药和总火药用量后，井底爆燃压力加载速率和各方向破裂压力均随第三级燃速火药质量比重的增加而呈现降低趋势，但变化不明显；而不同方向裂缝最终延伸长度对二、三级燃速火药的配比具有较强敏感性；在以多方向裂缝安全起裂为目标、设定一级燃速火药后，合理配比三种火药比单一配比高-中速、高-低速火药，可更有效地延长爆燃压裂过程的井底有效持压时间，从而可大幅扩展火药用量上限，提高爆燃压裂裂缝延伸规模。

Coupled loading simulation for combined pulse fracturing and the sensitivity analysis of different propellant ratios

In the present study, based on the physical process of combined pulse fracturing, we proposed a model for the coupling of the whole process of multi-pulse conflagration fracturing using different combinations of the multi-level pulse propellant conflagration loading model, the pressurized liquid column movement model, the perforation discharge model, the fracture initiation and the fracture dynamic extension model. Furthermore, we analyzed the wellbore pressure changes and the fractures propagation under single and combined propellants at different ratios. The calculated results demonstrated that fast deflagration fracturing could be initiated using combinations of the first-phase propellants with different burning rates and the multi-directional wellbore pressure was reached at once; a longer burning time of the propellant might be held to maintain the high pressure for the full extension of the fracture, using the second-and the third-phase propellants; when the amount of the first-phase propellants and the total amount of the propellants were determined, the deflagration loading rate and the multi-directional fracture initiation pressure tended to decrease slightly as the lowest burning rate of the third-phrase propellant's proportion rose up, though not obviously; the eventual extension lengths of the fracture in different directions were, however, very sensitive to the proportion of the second-and third-phase propellants. These results improved our understanding of the coupling mechanism of the combined pulse fracturing, and might be used to optimize the mass ratio of propellants.